Wavy Nanowires Research Articles

Medium entropy alloy wavy nanowires as highly effective and selective alcohol oxidation reaction catalysts for energy-saving hydrogen production and alcohol upgrade

Au-doped PtAgRhCu alloy wavy nanowire electrocatalysts deliver ultrahigh mass activity and selectivity for alcohol oxidation, enabling energy-saving hydrogen production and selective alcohol upgrading via alcohol-assisted water electrolysis.

Bifunctional Ultrathin RhRu0.5 -Alloy Nanowire Electrocatalysts for Hydrazine-Assisted Water Splitting.

Hydrazine-assisted water electrolysis offers a feasible path for low-voltage green hydrogen production. Herein, the design and synthesis of ultrathin RhRu0.5 -alloy wavy nanowires as bifunctional electrocatalysts for both the anodic hydrazine oxidation reaction (HzOR) and the cathodic hydrogen evolution reaction (HER) is reported. It is shown that the RhRu0.5 -alloy wavy nanowires can achieve complete electrooxidation of hydrazine with a low overpotential and high mass activity, as well as improved performance for the HER. The resulting RhRu0.5 bifunctional electrocatalysts enable, high performance hydrazine-assisted water electrolysis delivering a current density of 100mAcm-2 at an ultralow cell voltage of 54 mV and a high current density of 853mAcm-2 at a cell voltage of 0.6V. The RhRu0.5 electrocatalysts further demonstrate a stable operation at a high current density of 100mAcm-2 for 80 hours of testing period with little irreversible degradation. The overall performance greatlyexceeds that of the previously reported hydrazine-assisted water electrolyzers, offering a pathway for efficiently converting hazardous hydrazine into molecular hydrogen.

Ultrathin wavy nanowires of high-entropy alloy as cocktail solution in methanol oxidation reaction

High entropy alloys (HEAs) with adjustable composition and diverse surface active sites show good catalytic performance of methanol oxidation reaction (MOR). However, the synthesis and morphology control of HEA remains a challenge. Herein, we use a fast co-reduction method to synthesize a series of ultrathin wavy nanowires (WNWs) with an average diameter of 3–5 ​nm, including Pt-based and Pd-based binary alloys, and HEA with different pairs of immiscible elements. The catalytic properties of PtPdAgCuNi WNWs show that the mass activity and stability of PtPdAgCuNi WNWs is higher than Pt and Pd WNWs. Meanwhile we explored the cocktail effect among high entropy alloy elements through annealing. The cocktail effect among the metal elements in PtPdAgCuNi WNWs provided more active sites with increased metal-metal interactions, thus improving the catalytic efficiency.

Simulation of electrical conductivity for polymer silver nanowires systems

A simple model is developed for the conductivity of polymeric systems including silver nanowires (AgNWs). This model reveals the effects of interphase thickness, tunneling distance, waviness and aspect ratio of nanowires, as well as effective filler volume fraction on the percolation and electrical conductivity of AgNW-reinforced samples. The validity of this model is tested by using the measured data from several samples. Based on this model, the conductivity calculations are in proper accordance with the measured values. A large network and a low percolation onset are produced by nanowires with a high aspect ratio developing the nanocomposite conductivity. The results also show that a thicker interphase expands the network, thereby increasing the electrical conductivity. Furthermore, non-waved AgNWs exhibit more conductivity compared to wavy nanowires. It is concluded that the surface energies of polymer medium and nanowires have no effect on the conductivity of samples. On the other hand, the volume fraction and aspect ratio of nanowires, in addition to the interphase thickness and tunneling distance have the greatest influences on the conductivity of nanocomposites.

Ultrafast Synthesis of Wavy Gold‐Silver Alloy Nanowires with Tunable Diameters in the Range of 2‐10 nm via a Seed‐Mediated Co‐Reduction

AbstractWe report an ultrafast synthesis of wavy gold‐silver (AuAg) nanowires with tunable diameters via a seed‐mediated co‐reduction. The success of current strategy relies on the use of an elevated reaction temperature to accelerate the synthesis to be completed within several minutes and the use of Au seeds with controlled sizes to enable the manipulation over their diameters in the range of 2–10 nm. The presence of chloride‐contained quaternary ammonium surfactant and excessive reductant have been demonstrated to be critical for the high‐yield formation of AuAg products with the unique morphology of wavy nanowire. Due to the advantage in size control, the size effect on the plasmonic behavior of AuAg alloy wavy nanowires is investigated, where the products with sub‐5 nm diameter exhibit a broad shoulder absorbance peak in their spectrum.

Kinetically Manipulating the Nucleus Attachment to Create Atypical Defective Rh-Pt Alloyed Nanostructures as Active Electrocatalysts.

Defective metal nanostructures have attracted great attention due to the striking catalytic behavior of the defect sites. Atypical metal nanocrystals generated from attached nuclei can accommodate abundant grain boundaries (GBs) and twin boundaries (TBs). However, the understanding of their growth-mechanism and precisely synthetic control over such defective nanocrystals are still scarce. Herein, using the Rh-Pt nanoalloy as a model system, we systematically demonstrate that a prudent control of the reaction kinetics can manipulate the metal nucleation and nucleus attachment to create atypical nanocrystals, including small isolated nanoparticles (NPs), defect-rich wavy nanowires (WNWs), and {100} facet-bounded spliced nanocubes (SNCs). In the ethanol oxidation electrocatalysis, the Rh47 Pt53 WNWs featured with abundant TBs and GBs show the greatest mass activity (0.655 A ⋅ mg-1 Pt , 2.9 times to the commercial Pt/C) and durability. Our work captures the core of reaction kinetics on regulating the nucleus attachment and enables the rational control over the nanocrystal morphology and defect.

Pt3Ag alloy wavy nanowires as highly effective electrocatalysts for ethanol oxidation reaction

Direct ethanol fuel cell (DEFC) has received tremendous research interests because of the more convenient storage and transportation of ethanol vs. compressed hydrogen. However, the electrocatalytic ethanol oxidation reaction typically requires precious metal catalysts and is plagued with relatively high over potential and low mass activity. Here we report the synthesis of Pt3Ag alloy wavy nanowires via a particle attachment mechanism in a facile solvothermal process. Transmission microscopy studies and elemental analyses show highly wavy nanowire structures with an average diameter of 4.6 ± 1.0 nm and uniform Pt3Ag alloy formation. Electrocatalytic studies demonstrate that the resulting alloy nanowires can function as highly effective electrocatalysts for ethanol oxidation reactions (EOR) with ultrahigh specific activity of 28.0 mA/cm2 and mass activity of 6.1 A/mg, far exceeding that of the commercial Pt/carbon samples (1.10 A/mg). The improved electrocatalytic activity may be partly attributed to partial electron transfer from Ag to Pt in the Pt3Ag alloy, which weakens CO binding and the CO poisoning effect. The one-dimensional nanowire morphology also contributes to favorable charge transport properties that are critical for extracting charge from catalytic active sites to external circuits. The chronoamperometry studies demonstrate considerably improved stability for long term operation compared with the commercial Pt/C samples, making the Pt3Ag wavy nanowires an attractive electrocatalyst for EOR.

Au-Doped intermetallic Pd3Pb wavy nanowires as highly efficient electrocatalysts toward the oxygen reduction reaction

Au-Doped intermetallic Pd3Pb wavy nanowires were synthesized and exhibited substantially enhanced properties for the oxygen reduction reaction relative to commercial Pt/C.

Wavy PtCu alloy nanowire networks with abundant surface defects enhanced oxygen reduction reaction

Bimetallic platinum-copper (Pt-Cu) alloy nanowires have emerged as a novel class of fuel cell electrocatalysts for oxygen reduction reaction (ORR) due to their intrinsic high catalytic activity and durability, but preparing such electrocatalysts with clean surface via facile method is still a challenge. Herein, PtCu alloy with nanowire networks (NWNs) structure is obtained by a simple modified polyol method accompanied with a salt-mediated self-assembly process in a water/ethylene glycol (EG) mixing media. The formation mechanism of PtCu NWNs including the morphological evolution and the relevant experimental parameters has been investigated systematically. We propose that a micro-interface in H2O-EG media formed with the assistance of disodium dihydrogen pyrophosphate (Na2H2P2O7) and its unique nature of coordinating with Pt2+ or Cu2+ play critical roles in the formation of NWNs. When tested as ORR catalyst, the PtCuNWNs/C exhibits much higher activity and durability than that of PtNWNs/C and commercial Pt/C, even exceeding the target of DOE in 2020. The excellent performance of PtCuNWNs/C could be attributed to the unique structure of NWNs with 2.4 nm ultrathin wavy nanowires and plentiful surface defects and the modified electronic effect caused by alloying with Cu atoms.

Ultrathin wavy Rh nanowires as highly effective electrocatalysts for methanol oxidation reaction with ultrahigh ECSA

Direct methanol fuel cells (DMFCs) have received tremendous research interests because of the facile storage of liquid methanol vs. hydrogen. However, the DMFC today is severely plagued by the poor kinetics and rather high overpotential in methanol oxidation reaction (MOR). Here we report the investigation of the ultrathin Rh wavy nanowires as a highly effective MOR electrocatalyst. We show that ultrathin wavy Rh nanowires can be robustly synthesized with 2–3 nm diameters. Electrochemical studies show a current peak at the potential of 0.61 V vs. reversible hydrogen electrode (RHE), considerably lower than that of Pt based catalysts (~ 0.8–0.9 V vs. RHE). Importantly, with ultrathin diameters and favorable charge transport, the Rh nanowires catalysts exhibit an ultrahigh electrochemically active surface area determined from CO-stripping (ECSACO) of 144.2 m2/g, far exceeding that of the commercial Rh black samples (20 m2/g). Together, the Rh nanowire catalysts deliver a mass activity of 722 mA/mg at 0.61 V, considerably higher than many previously reported electrocatalysts at the same potential. The chronoamperometry studies also demonstrate good stability and CO-tolerance compared with the Rh black control sample, making ultrathin Rh wavy nanowires an attractive electrocatalyst for MOR.

Ultrathin Ir nanowires as high-performance electrocatalysts for efficient water splitting in acidic media.

The search for active and stable bifunctional electrocatalysts toward acidic overall water splitting is under increasing demand for the development of polymer electrolyte membrane (PEM) electrolyzers. However, developing bifunctional electrocatalysts with Pt-like activity and superior stability under acidic media still remains a big challenge. Herein, we report a successful synthesis of Ir wavy nanowires with an ultrathin diameter of 1.7 nm through a simple wet-chemical approach. Benefiting from the unique morphology with high aspect ratios and a large specific surface area, the as-synthesized ultrathin Ir wavy nanowires exhibit enhanced activity and durability for both the oxygen evolution reaction and the hydrogen evolution reaction in acidic electrolytes. Moreover, when used for overall acidic water splitting, a current density of 10 mA cm-2 is achieved at only a cell voltage of 1.62 V in 0.1 M HClO4 electrolyte with long-term stability. In view of the excellent electrochemical water splitting performance and superior stability in acidic electrolytes, we believe that the obtained Ir wavy nanowires could be potential alternative catalysts toward PEM water electrolysis.

Finely Composition-Tunable Synthesis of Ultrafine Wavy PtRu Nanowires as Effective Electrochemical Sensors for Dopamine Detection

Preparing Pt-based one-dimensional (1D) ultrafine nanowires with abundant structural defects/grain boundaries and exploring their novel applications have attracted great interest in real-world applications. Here we introduce an environmentally friendly, facile aqueous solution approach to directly prepare a series of sub-3.0 nm PtRu ultrafine wavy nanowires. Characterizations show that the PtRu nanowires are alloy polycrystalline structures with abundant structural defects/grain boundaries. We first introduce the as-synthesized PtRu nanowires into electrochemical biosensors for the detection of DA and find that the Pt7Ru3 nanowires exhibit excellent electrocatalytic activity to DA with fast response, ultralow limit of detection, and excellent selectivity at a potential of 0.3 V in 0.1 M phosphate buffered solution (pH 7.2). This study shows an effective approach to the development of ultrafine PtRu nanowires as electrocatalysts for electrochemical nonenzymatic dopamine biosensors.

Carbon Monoxide-Assisted Synthesis of Ultrathin PtCu3 Alloy Wavy Nanowires and Their Enhanced Electrocatalysis.

Glucose sensing that is not influenced by the presence of chloride, uric acid, ascorbic acid and dopamine is achieved on ultrathin PtCu3 alloy wavy nanowires (WNWs). These WNWs are synthesized by a facile, one-pot, templateless hydrothermal method in an atmosphere of CO, which is critical to the formation process. Their structural properties, including the abundance of twinning defects, make the as-prepared PtCu3 WNWs excellent electrocatalysts for methanol oxidation as well as great sensors for glucose.

Hydrogen gas-assisted synthesis of worm-like PtMo wavy nanowires as efficient catalysts for the methanol oxidation reaction

A facile method for one-pot synthesis of worm-like PtMo wavy nanowires under hydrogen pressure is developed. The as-made catalyst shows superior catalytic activity and durability towards the methanol oxidation reaction.

Trimetallic PtSnRh Wavy Nanowires as Efficient Nanoelectrocatalysts for Alcohol Electrooxidation.

The design and creation of efficient catalysts for alcohol oxidation reaction has attracted great research attention because alcohols are promising fuels for direct fuel cell reactions because of their high energy density, easy storage, and transportation. We herein report an efficient strategy that allows the preparation of ternary PtSnM (M=Co, Ni, and Rh) wavy nanowires (WNWs) with ultrathin diameter of only around 2 nm and tunable compositions in high yield. Detailed catalytic studies show that all the ternary WNWs exhibit high performance for ethanol oxidation reaction (EOR) and methanol oxidation reaction (MOR), and their performance shows interesting composition-dependent electrocatalytic activity with PtSnRh WNWs having the best activity for both EOR and MOR. The PtSnRh WNWs are also more stable than commercial Pt/C catalyst, as revealed by long-time chronoamperometric (CA) measurements. The present work highlights the use of multimetallic WNWs as highly active and durable nanocatalysts in enhancing alcohol electrooxidation, which will open a new way in tuning 1D multimetallic nanostructures for boosting other fuel cell reactions, various heterogeneous reactions, and beyond.

Facile synthesis of ultrathin bimetallic PtSn wavy nanowires by nanoparticle attachment as enhanced hydrogenation catalysts.

Ultrathin wavy nanowires represent an emerging class of nanostructures that exhibit unique catalytic, magnetic, and electronic properties, but the controlled production of bimetallic wavy nanowires remains a significant challenge. Ultrathin bimetallic PtSn nanowires have been prepared with high yield and featuring a highly wavy structure. Owing to the ultrathin nature and unique electronic properties of these PtSn wavy nanowires, they exhibit improved catalytic performance for the hydrogenation of nitrobenzene, as well as for the hydrogenation of styrene. These results suggest a new strategy to prepare highly active catalysts through defect engineering and can significantly impact broad practical applications.

High density catalytic hot spots in ultrafine wavy nanowires.

Structural defects/grain boundaries in metallic materials can exhibit unusual chemical reactivity and play important roles in catalysis. Bulk polycrystalline materials possess many structural defects, which is, however, usually inaccessible to solution reactants and hardly useful for practical catalytic reactions. Typical metallic nanocrystals usually exhibit well-defined crystalline structure with few defects/grain boundaries. Here, we report the design of ultrafine wavy nanowires (WNWs) with a high density of accessible structural defects/grain boundaries as highly active catalytic hot spots. We show that rhodium WNWs can be readily synthesized with controllable number of structural defects and demonstrate the number of structural defects can fundamentally determine their catalytic activity in selective oxidation of benzyl alcohol by O2, with the catalytic activity increasing with the number of structural defects. X-ray photoelectron spectroscopy (XPS) and cyclic voltammograms (CVs) studies demonstrate that the structural defects can significantly alter the chemical state of the Rh WNWs to modulate their catalytic activity. Lastly, our systematic studies further demonstrate that the concept of defect engineering in WNWs for improved catalytic performance is general and can be readily extended to other similar systems, including palladium and iridium WNWs.

Polyol Synthesis of Ultrathin Pd Nanowires via Attachment‐Based Growth and Their Enhanced Activity towards Formic Acid Oxidation

Palladium wavy nanowires with an ultrathin diameter of 2 nm are synthesized using the polyol method without the involvement of any template. The success of this synthesis relies on the use of a suitable precursor that could be reduced instantaneously to generate a large number of small Pd nanoparticles. Due to a quick depletion of precursor, the small nanoparticles were unable to grow in size through atomic addition. In the case of low surface charges and high surface energies, these small nanoparticles were forced to coalesce into ultrathin nanowires with a wavy morphology via an attachment mechanism. Thanks to the unique structure and involvement of twin defects, the as‐obtained Pd ultrathin nanowires show a catalytic current density of 2.5 times higher than the conventional Pd/C catalyst towards formic acid oxidation. This work not only offers a powerful route to the synthesis of nanowires through attachment‐based growth but also opens the door to the rational design and fabrication of novel metal nanostructures with enhanced properties.

Cover Picture: Seed-Mediated Synthesis of Single-Crystal Gold Nanospheres with Controlled Diameters in the Range 5-30 nm and their Self-Assembly upon Dilution (Chem. Asian J. 4/2013)

Gold nanospheres with diameters precisely controlled in the range of 5–30 nm were synthesized using a successive, seed-mediated growth, as reported by Younan Xia et al. in their Full Paper on page 792 ff. The gold nanospheres were found to self-assemble into dimers, larger aggregates, and wavy nanowires when they were diluted to different volumes with deionized water.

Seed‐Mediated Synthesis of Single‐Crystal Gold Nanospheres with Controlled Diameters in the Range 5–30 nm and their Self‐Assembly upon Dilution

Single-crystal gold nanospheres with controlled diameters in the range 5-30 nm were synthesized by using a facile approach that was based on successive seed-mediated growth. The key to the success of this synthesis was the use of hexadecyltrimethylammonium chloride (CTAC) as a capping agent and a large excess of ascorbic acid as a reductant to ensure fast reduction and, thus, single crystallinity and a spherical shape of the resultant nanoparticles. The diameters of the gold nanospheres could be readily controlled by varying the amount of seeds that were introduced into the reaction system. The gold nanospheres could be produced with uniform diameters of up to 30 nm; thus, their localized surface plasmon resonance properties could be directly compared with the results that were obtained from theoretical calculations. Interestingly, we also found that these gold nanospheres self-assembled into dimers, larger aggregates, and wavy nanowires when they were collected by centrifugation, dispersed in deionized water, and then diluted to different volumes with deionized water.